BIO 111 - Chapter 5

Uniporter

A carrier protein in a cell's membrane that transports only a single type of molecule or ion.

Antiporter

A carrier protein in a cell's membrane that transports two molecules in opposite directions across the membrane.

Symporter

A carrier protein in a cell's membrane that transports two molecules or ions in the same direction across the membrane.

Concentration gradient

A difference in concentration of a substance from one location to another, often across a membrane.

Aquaporin

A membrane channel that allows water to cross the membrane more easily than by diffusion through the membrane.

Transporter

A membrane protein that binds a solute and undergoes a conformational change to allow the movement of the solute across a membrane.

Carrier protein

A membrane protein that binds to a specific molecule that cannot cross the membrane and allows passage through the membrane.

Fluid mosaic model

A model that describes the structure of cell membranes. In this model, a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell.

Solute

A molecule dissolved in some solution; as a general wurle, solutes dissolve only in solutions of similar polarity; for example, glucose (polar) dissolves in (forms hydrogen bonds with) water (also polar), but not in vegetable oil (nonpolar).

Anions

A negatively charged ion.

Cation

A positively charged ion.

Extrusion

A process where a cell exports large particles or organelles: transports them through its cell membrane to the outside. Requires energy.

Clathrin

A protein located just inside the plasma membrane in eukaryotic cells, in indentations called clathrin-coated pits.

Peripheral protein

A protein that temporarily adheres to the biological membrane, either to the lipid bilayer or to integral proteins by a combination of hydrophobic, electrostatic, and other non-covalent interactions.

Paramecium

A single-celled freshwater animal that has a characteristic slipperlike shape and is covered with cilia.

Isotonic

A solution having the same concentration of solutes as the cell. A cell in an __________ solution takes in and loses the same amount of water.

Aqueous solution

A solution in which the solvent is water. It is usually shown in chemical equations by appending (aq) to the relevant formula. For example, a solution of ordinary table salt, or sodium chloride (NaCl), in water would be represented as NaCl(aq).

Hypertonic

A solution with a higher concentration of solutes than the cell. A cell in a hypertonic solution tends to lose water by osmosis.

Hypotonic

A solution with a lower concentration of solutes than the cell. A cell in a ___________ solution tends to take in water by osmosis.

Channel protein, Ion channel

A transmembrane protein with a hydrophilic interior that provides an aqueous channel allowing diffusion of species that cannot cross the membrane. Usually allows passage of specific ions such as K+, Na+, or Ca2+ across the membrane.

Exocytosis

A type of bulk transport out of cells in which a vacuole fuses with the plasma membrane, discharging the vacuole's contents to the outside.

Transmembrane protein

A type of membrane protein spanning the entirety of the biological membrane to which it is permanently attached. That is, transmembrane proteins span from one side of a membrane through to the other side of the membrane.

Integral membrane proteins (IMP)

A type of membrane protein that is permanently attached to the biological membrane. All transmembrane proteins are IMPs, but not all IMPs are transmembrane proteins.

Fatty acid desaturases

An enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond.

Pore protein, Porins

Beta barrel proteins that cross a cellular membrane and act as a pore through which molecules can diffuse. Unlike other membrane transport proteins, porins are large enough to allow passive diffusion, i.e., they act as channels that are specific to different types of molecules.

Facilitated diffusion

Carrier-assisted diffusion of molecules across a cellular membrane through specific channels from a region of higher concentration to one of lower concentration; the process is driven by the concentration gradient and does not require cellular energy from ATP.

Gated channel

Channel through a membrane that can be opened or closed by chemical or electrical events.

Selectively permeable

Condition in which a membrane is permeable to some substances but not to others.

Phagocytosis

Endocytosis of a solid particle; the plasma membrane folds inward around the particle - which may be another cell - and engulfs it to form a vacuole.

Transmembrane domain

Hydrophobic region of a transmembrane protein that anchors it in the membrane. Often composed of a-helics, but sometimes utilizing B-pleated sheets to form a barrel-shaped pore.

Ion channels

Pore-forming membrane proteins whose functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane, controlling the flow of ions across secretory and epithelial cells, and regulating cell volume.

Receptor-mediated endocytosis

Process by which specific macromolecules are transported into eukaryotic cells at clathrin-coated pits, after binding to specific cell-surface receptors.

Glycoprotein

Protein molecule modified within the Golgi complex by having a short sugar chain - polysaccharide - attached.

Membrane potentials

Ratio of inside versus outside concentration of potassium, sodium, chloride and other ions in diffusible tissues or cells. Also called transmembrane and resting potentials, they are measured by recording electrophysiologic responses in voltage-dependent ionic channels of (e.g.) nerve, muscle and blood cells as well as artificial membranes.

Phospholipid

Similar in structure to a fat, but having only two fatty acids attached to the glycerol backbone, with the third space linked to a phosphorylated molecule; contains a polar hydrophilic "head" end - phosphate group - and a nonpolar hydrophobic "tail" end - fatty acids.

Saturation

The act, process, or result of saturating a substance, or of combining it to its fullest extent.

Hyperosmotic

The condition in which a ___________ solution has a higher osmotic concentration than that of a second solution.

Hypoosmotic

The condition in which a ___________ solution has a lower osmotic concentration than that of a second solution.

Isosmotic

The condition in which the osmotic concentrations of two solutions are equal, so that no net water movement occurs between them by osmosis.

Osmosis

The diffusion of water across a selectively permeable membrane - a membrane that permits the free passage of water but prevents or retards the passage of a solute; in the absence of differences in pressure or volume, the net movement of water is from the side containing a lower concentration of solute to the side containing a higher concentration.

Turgor pressure

The internal pressure inside a plant cell, resulting from osmotic intake of water, that presses its cell membrane tightly against the cell wall, making the cell rigid. Also known as hydrostatic pressure.

Coupled transport

The linked, simultaneous transport of two substances across a cell membrane, or another intracellular membrane.

Phospholipid bilayer

The main component of cell membranes; phospholipids naturally associate in a bilayer with hydrophobic fatty acids oriented to the inside and hydrophilic phosphate groups facing outward on both sides.

Solvent

The medium in which one or more solutes is dissolved.

Bulk transport

The movement of large quantities of materials into or out of cells, endocytosis and exocytosis, respectively.

Passive transport

The movement of substances across a cell's membrane without the expenditure of energy.

Diffusion

The net movement of dissolved molecules or other particles from a region where they are more concentrated to a region where they are less concentrated.

Osmotic pressure

The potential pressure developed by a solution separated from pure water by a differentially permeable membrane. The higher the solute concentration, the greater the osmotic potential of the solution; also called osmotic potential.

Pinocytosis

The process of fluid uptake by endocytosis in a cell.

Osmotic concentration

The property of a solution that takes into account all dissolved solutes in the solution; if two solutions with different osmotic concentrations are separated by a water-permeable membrane, water will move from the solution with lower osmotic concentration to the solution with higher osmotic concentration.

Active transport

The pumping of individual ions or other molecules across a cellular membrane from a region of lower concentration to one of higher concentration (i.e., against a concentration gradient); this transport process requires energy, which is typically supplied by the expenditure of ATP.

Countertransport

The transport of one substance across a membrane, coupled with the simultaneous transport of another substance across the same membrane in the opposite direction.

Endocytosis

The uptake of material into cells by inclusion within an invagination of the plasma membrane; the uptake of solid material is phagocytosis, and that of dissolved material is pinocytosis.

Sodium-potassium pump

Transmembrane channels engaged in the active - ATP-driven - transport of Na+, exchanging them for K+, where both ions are being moved against their respective concentration gradients; maintains the resting membrane potential of neurons and other cells.

Glycolipid

Lipid molecule modified within the Golgi complex by having a short sugar chain - polysaccharide - attatched.

Lipid rafts

Originally defined as membrane domains, i.e., ordered structures created as a consequence of the lateral segregation of sphingolipids and differing from the surrounding membrane in their molecular composition and properties.